1. Field of the Invention
The present invention relates to an automatic focusing apparatus, an imaging apparatus, a focusing control method, and a program, and more particularly, to a technology relating to an automatic focusing (AF) which is utilized for electronic still cameras and video cameras.
2. Description of the Related Art
Conventionally, when an automatic focus (sometimes written as AF) is performed in electronic still cameras or video cameras, there has been used a system in which a lens position, at which a high-frequency component of a luminance signal obtained from an image sensor using a charge-coupled device (CCD) or the like becomes maximal, is regarded as an in-focus position. As one of the systems, the following scanning system is known.
More specifically, while driving a lens over the whole range of the focus detection range an evaluation value (sometimes written as a focus evaluation value), which is obtained based on the high-frequency component of the luminance signal obtained from the image sensor, continues to be stored each time, and a lens position corresponding to the maximum value among the stored values is determined as an in-focus position.
Further, there is known a hill-climbing system (sometimes referred to as a continuous AF), in which, when the lens is moved in a direction in which a focus evaluation value increases, a position at which the focus evaluation value becomes maximal is determined as an in-focus position.
Furthermore, there is a method for limiting a focus detection range of an AF by a scanning system to be performed after the imaging preparation instruction is issued by performing the continuous AF before the imaging preparation instruction to maintain an in-focus state, and thereby shortening a time taken for an AF operation.
However, in the conventional camera, there is a problem that, when a zoom position is at a telephoto side, a field of view will be displaced significantly by slightly moving the camera. For this reason, it is difficult and takes a time to bring again the object, which has once gone out of the field of view, into the field of view, at the time of telephoto imaging of the camera having a high-magnification zoom lens, and in some cases, a distance of the object has changed greatly, and the object has gone out of focus, when the field of view adjustment is achieved.